1. Field of the Invention
The present invention relates to a projection apparatus, a projection method, and a computer program for controlling the projection apparatus.
2. Description of the Related Art
Projection apparatuses generally called projector have become popular as apparatuses for projecting images on a screen. For example, some projectors adopt a single-plate DMD (Digital Micromirror Device™), as one projection method. Such a projector comprises a minute mirror (DMD) whose angle can be controlled. By focusing light, which passes through a rapidly rotating color wheel (color filter) on which red (R), green (G), and blue (B) are arranged, on the DMD, this projector can continuously display images corresponding to these colors respectively. In projecting a black image, the projector uses the DMD to reflect light toward a light absorption plate, and reduces the amount of projection light to be directed to the screen. In other words, when a black image is projected, there exists unused light (useless light) that is not projected on the screen.
For example, Unexamined Japanese Patent Application KOKAI Publication No. 2005-107400 discloses a projector using a pattern-variable color wheel which has regions though which light having the three primary colors of R, G, and B can pass respectively, and a region through which white light can pass. According to this publication, the projector can dynamically change the color tones even in the midst of a projection operation without giving people a feeling of strangeness, by switching the regions of the color wheel to let light pass through by a motor.
A projector using such a color wheel needs to synchronize the control on the rotation of the color wheel and the control by a light modulation device such as a DMD, etc. on the proceeding direction of transmitting light. A conventional method of synchronizing the color wheel and the light modulation device has been to detect a white (W) portion of the color wheel by a photo coupler.
However, since color wheels need individual adjustments because they have manufacturing errors or differ in assembly accuracy, they require a lot of care and cost much in manufacturing. Further, in order to use a pattern-variable color wheel as disclosed in the above-indicated publication, it is necessary to control the color wheel by accurately knowing the boundary between the regions of the respective colors. It has been difficult to perform such precise control.
The present invention provides a projection apparatus, a projection method, and a computer program for solving the above-described problems.